Once behavior has been distinguished largely on the
basis of structural characteristics, it becomes easier to
assume that different theories or explanations are required
for the development of each type of behavior. For example,
Piaget's theory intends to explain cognitive development,
Freud's theory intends to explain social development,
both Piaget and Kohlberg have theories of moral development,
and there are different theories of emotional development,
language development, and so on. Even within
single theoretical systems, structurally differentiated behaviors
are afforded different explanations. In Piaget's
theory, for example, there are different mental structures
to explain object permanence, conservation, egocentrism,
and so on. In fact, the entire field of child development
implies a domain that is functionally distinct from adult
psychology, as if each were governed by different psycho